A drilling fluid or mud is a specially designed fluid that is circulated through a wellbore as the wellbore is being drilled to facilitate the drilling operation. Drilling fluids facilitate the removal of drill cuttings from the wellbore, cool and lubricate the drill bit, aid in supporting the drill pipe and drill bit, and provide a hydrostatic head to maintain the integrity of the wellbore walls thereby minimizing the potential for well blowouts. Specific drilling fluid systems are selected to optimize a drilling operation in accordance with the characteristics of a particular geological formation.
Oil or synthetic-based mud, or invert emulsions, are normally used to drill swelling or sloughing shale, salt, gypsum, anhydrite or other evaporate formations, hydrogen sulfide-containing formations, and hot (greater than about 300° F.) holes, but may be used in other holes penetrating a subterranean formation as well. This class of drilling fluids typically contains oil or a synthetic oil or other synthetic material or synthetic fluid (“synthetic”) as the continuous phase and may also contain water which is dispersed in the continuous phase by emulsification so that there is no distinct layer of water in the fluid. The term “oil mud” or “oil or synthetic-based mud” typically means an invert oil mud emulsion or invert emulsion. An all oil mud simply comprises 100% oil by volume as the liquid phase; that is, there is no aqueous internal phase. An invert emulsion drilling fluid may commonly comprise between about 50:50 to 95:5 by volume oil phase to water phase.
Invert emulsions used in drilling typically comprise: a base oil or synthetic fluid for the external phase; a saline, aqueous solution for the internal phase (typically a solution comprising about 30% calcium chloride); and other agents or additives for suspension, fluid loss, density, oil-wetting, emulsification, filtration, and rheology control.
U.S. Pat. No. 7,247,604 generally relates to alkanolamide based emulsifiers obtained by transamidification of fatty acid esters and mono-alcohols or oils of a plant of animal origin (triglyceride) with alkanoamine. The oil based drilling fluid made with the emulsifier and co-surfactant was claimed having temperature-stable, non-toxic to the environment, and high temperature and high pressure (HTHP) well drilling, completion or workover application properties.
U.S. Pat. Nos. 4,508,628 and 4,575,428 disclose invert emulsion drilling fluid emulsfiers derived from polyamines. The preferred polyamide emulsifiers are prepared by first reacting a polyamine with fatty acid in order to form a amidoamine and thereafter reacting the amidoamine intermediate with a dicarboxylic acid (in U.S. Pat. No. 4,508,628) or tricarboxylic acid (in U.S. Pat. No. 4,575,428). It is apparent from the disclosure of the documents that short chain polyamines containing no alkoxy groups are contemplated.
U.S. Pat. No. 3,169,113 discloses emulsifiers for water-in-oil acidic fracturing fluids. The disclosed emulsifier has two components: (a) a 9-18 carbon monocarboxylic acid fatty acid salt of a partial amide of a polyalkyllene polyamine with 2-6 carbon alkylene groups and 3-5 amino nitrogens in which at least two amino groups are amidified with 9-18 carbon monocarboxylic fatty acids and wherein there is at least one nonamidified amino group forming a salt with the acid and, (b) a polyamide of an alkylene polyamine with 2-6 carbon alkylene groups and 2-5 amino nitrogens and a 9-18 carbon monocarboxylic fatty acid.
U.S. Pat. No. 4,501,672 discloses fluid loss reducing additives for oil-based working fluids. The additive is obtained by reacting 1 mole of dialkylene triamine with 2 moles of fatty acid. Example 1 specifically covers the bridging of diethylenetriamine dioleylamide with maleic anhydride.
WO 89/11516 discloses oil-based emulsifiers for drilling fluids that are the reaction product of one or two moles of an amide-amine or a hydroxylalkylamide with one to five moles of a dicarboxylic acid or an acid anhydride. Starting on page 5 of this document it is apparent that the use of short chain polyamines with no alkoxy groups is contemplated.
U.S. Pat. No. 4,658,036 discloses an invert emulsion and a process of preparing same. The emulsifiers are prepared by reacting at least one tall oil fatty acid with acrylic acid, maleic anhydride, or fumaric acid, followed by reaction with diethylenetriamine and at least one tall oil fatty acid in order to give the invert emulsifier.
With space at some well sites limited, such as on offshore platforms, and with increasing costs of transport of materials to a well site, there is industry-wide interest, on-going need for more efficient and concentrated drilling fluid additives and for drilling fluids which can be formulated and maintained with fewer additives in lesser amounts than commonly utilized with prior art drilling fluids.